The invention relates to a casting roll for the continuous casting of thin metallic strips, in particular of steel strips, in a two-roll or one-roll casting installation. The casting roll has a roll core with an outer lateral surface and an annular roll shell which surrounds the roll core, is shrunk on and has an inner lateral surface and having a central casting-roll axis, and to a process for producing a casting roll of this type.
Casting rolls of this type are used to produce metal strip with a thickness of up to 10 mm. Liquid metal is applied to the surface of at least one casting roll, where it at least partially solidifies and is deformed into the desired strip format. If the metal melt is applied predominantly to a casting roll, one speaks of one-roll casting processes. If the metal melt is introduced into a casting nip which is formed by two casting rolls arranged at a distance from one another, with the metal melt solidifying at the two casting-roll surfaces and a metal strip being formed therefrom, one speaks of two-roll casting processes. In these production processes, large quantities of heat have to be dissipated from the casting roll surface into the interior of the casting roll within a short time. This is achieved by the casting roll being equipped with an outer roll shell made from a particularly thermally conductive material, preferably copper or a copper alloy, and internal cooling with a cooling-water circuit. Casting rolls of this type have already been described, for example in U.S. Pat. No. 5,191,925 or DE-C 41 30 202.
U.S. Pat. No. 5,191,925 has disclosed a casting roll in which two annular roll shells are drawn onto a roll core equipped with cooling ducts, and the two roll shells are joined to one another by a welded joint, or one roll shell is produced by electrodeposition on the other roll shell.
DE-C 41 30 202 has disclosed a casting roll in which a join is produced between a roll core and a roll shell by brazing, with a suitable brazing solder, preferably in the form of a strip of this brazing solder, having to be applied and secured between the roll core and the roll shell prior to assembly. The roll shell is drawn onto the roll core by means of a thermal shrinking process and in this way a provisional join is formed, followed by the more time-consuming brazing process.
In conventional continuous-casting installations, it is known for the continuous-casting mold to be followed, over the path of the strand, by supporting and guide rollers, which are subject to significantly lower thermal loads, for supporting the cast strand (DE-C 40 27 225). In the case of these supporting and guide rollers, a roller shell is drawn onto a roller core by means of a shrink-fit connection, with a mating fit which complies with the appropriate standards then being provided between the roller shell and roller core.
On account of the high productivity required of the installation, extreme cyclical thermal loads are produced at the roll shell of casting rolls for the direct casting of metal strips, in particular when steel is being cast. It is known that a specific dissipation of heat of up to 15 MW/m2 and more has to be effected through the roll shell. In casting roll structures of the type described in the introduction, which are usually formed by a copper tube shrunk onto a steel core, the local, cyclically occurring circumferential stress fluctuations associated with the thermal loads give rise to circumferential forces which can cause the copper shell to migrate on the steel core. This migrating movement leads to changes in adhesion at the contact surface between copper shell and steel core, typically leading to rapid aging of the bonded joint. As a result, the service life of the copper shell or the bonded joint is significantly reduced.
Even the proposed brazed joint, in addition to being complex to produce, is unsuitable for preventing a migratory movement of the roll shell of this type in the long term under the locally high thermal loads which occur.